Thermal stability of poly(methyl methacrylate)

Summary The average solid-state molecular structures of end-groups generated through chain termination reactions in the polymerization of methyl methacrylate have been derived from published crystallographic data. Evidence is provided for the reduced stability of the head-head chain-termination configuration and in support of the postulate that it is a preferred site of chain scission. Comparable evidence for the unsaturated end group has not been found.     

Retrenching partial requirements into system definitions: a simple feature interaction case study

In conventional model-oriented formal refinement, the abstract model is supposed to capture all the properties of interest in the system, in an as-clutter-free-as-possible manner. Subsequently, the refinement process guides development inexorably towards a faithful implementation. However, refinement says nothing about how to obtain the abstract model in the first place. In reality developers experiment with prototype models and their refinements until a workable arrangement is discovered.Retrenchment is a formal technique intended to capture some of the informal approach to a refinable abstract model in a formal manner that will integrate with refinement. This is in order that the benefits of a formal approach can migrate further up the development hierarchy. The basic ideas of retrenchment are presented, and a simple telephone system feature interaction case study is elaborated. This illustrates not only how retrenchment can relate incompatible and partial models to a more definitive consolidated model during the development of the contracted specification, but also that the same formalism is applicable in a re-engineering context, where the subsequent evolution of a system may be partly incompatible with earlier design decisions. The case study illustrates how the natural method of composing retrenchments can give results that are too liberal in certain cases, and stronger laws of composition are derived for systems possessing suitable properties. It is shown that the methodology can encompass more ad hoc and custom-built techniques such as Zave's layered feature engineering approach to applications exhibiting a feature-oriented architecture (such as telephony).

Formalising the Hybrid ERTMS Level 3 specification in iUML-B and Event-B

We demonstrate refinement-based formal development of the hybrid, ‘fixed virtual block’ approach to train movement control for the emerging European Rail Traffic Management System (ERTMS) level 3. Our approach uses iUML-B diagrams as a front end to the Event-B modelling language. We use abstraction to verify the principle of movement authority before gradually developing the details of the Virtual Block Detector component in subsequent refinements, thus verifying that it preserves the safety properties. We animate the refined models to demonstrate their validity using the scenarios from the Hybrid ERTMS Level 3 (HLIII) specification. We reflect on our team-based approach to finding useful modelling abstractions and demonstrate a systematic modelling method based on the state and class diagrams of iUML-B. The component and control flow architectures of the application, its environment and interacting systems emerge through the layered refinement process. The runtime semantics of the specification’s state-machine behaviour are modelled in the final refinements. We discuss how the model could be used to generate an implementation using code generation tools and techniques.

     

Fast test suite-driven model-based fault localisation with application to pinpointing defects in student programs

Fault localisation, i.e. the identification of program locations that cause errors, takes significant effort and cost. We describe a fast model-based fault localisation algorithm that, given a test suite, uses symbolic execution methods to fully automatically identify a small subset of program locations where genuine program repairs exist. Our algorithm iterates over failing test cases and collects locations where an assignment change can repair exhibited faulty behaviour. Our main contribution is an improved search through the test suite, reducing the effort for the symbolic execution of the models and leading to speed-ups of more than two orders of magnitude over the previously published implementation by Griesmayer et al. We implemented our algorithm for C programs, using the KLEE symbolic execution engine, and demonstrate its effectiveness on the Siemens TCAS variants. Its performance is in line with recent alternative model-based fault localisation techniques, but narrows the location set further without rejecting any genuine repair locations where faults can be fixed by changing a single assignment. We also show how our tool can be used in an educational context to improve self-guided learning and accelerate assessment. We apply our algorithm to a large selection of actual student coursework submissions, providing precise localisation within a sub-second response time. We show this using small test suites, already provided in the coursework management system, and on expanded test suites, demonstrating the scalability of our approach. We also show compliance with test suites does not reliably grade a class of “almost-correct” submissions, which our tool highlights, as being close to the correct answer. Finally, we show an extension to our tool that extends our fast localisation results to a selection of student submissions that contain two faults.

     

Vegetation of central Florida's East coast: The distribution of six vegetational complexes of Merritt Island and Cape Canaveral Peninsula

Several discrete vegetation types on Merritt Island and Cape Canaveral barrier island were delineated by use of LANDSAT satellite data. Categories of vegetation based upon community structure and the presence or absence of water were determined in a two-stage analysis. First, a detailed map covering 52 km² was prepared using conventional methods (i.e., site visits, high-resolution aerial photographs, and direct aerial investigations). Then an interactive computerized system (Image 100) was used to analyze LANDSAT data for the same area. Six plant community forms, differing by vegetation height, canopy openness and the amount of water visible from the air, were mapped. These physiognomic characteristics were used because they often influenced the light reflected from an area more than did the floristic composition. The computer was adjusted to detect all regions with similar light-reflectance characteristics; the search limits were then manually adjusted until the regions detected by the computer agreed with the known distribution of vegetation appearing in the detailed vegetation map. These limits were applied to the entire coastal area and the computer maps printed. The resulting distribution maps were spot checked for accuracy by site visitation. The areas identified by the method were indicative of discrete physiognomic types which in turn were easily related to major plant association types. Expression of the computer classification technique's full potential depends on the intimate participation of trained botanists, and the prior completion of extensive field studies.     

Viscosity modification of flash pyrolysis tars

A study was made of the effect of a number of additives on the viscosity of a characteristic tar produced by the flash pyrolysis of indigenous Australian coals. The results indicate that aliphatic compounds are more effective than aromatic compounds in lowering the viscosity. This observation is of significance in the selection of suitable recycle solvents and the dissolution of aged tars.     

Towards an integrated formal method for verification of liveness properties in distributed systems: with application to population protocols

State-based formal methods [e.g. Event-B/RODIN (Abrial in Modeling in Event-B—system and software engineering. Cambridge University Press, Cambridge, 2010; Abrial et al. in Int J Softw Tools Technol Transf (STTT) 12(6):447–466, 2010)] for critical system development and verification are now well established, with track records including tool support and industrial applications. The focus of proof-based verification, in particular, is on safety properties. Liveness properties, which guarantee eventual, or converging computations of some requirements, are less well dealt with. Inductive reasoning about liveness is not explicitly supported. Liveness proofs are often complex and expensive, requiring high-skill levels on the part of the verification engineer. Fairness-based temporal logic approaches have been proposed to address this, e.g. TLA Lamport (ACM Trans Program Lang Syst 16(3):872–923, 1994) and that of Manna and Pnueli (Temporal verification of reactive systems—safety. Springer, New York, 1995). We contribute to this technology need by proposing a fairness-based method integrating temporal and first-order logic, proof and tools for modelling and verification of safety and liveness properties. The method is based on an integration of Event-B and TLA. Building on our previous work (Méry and Poppleton in Integrated formal methods, 10th international conference, IFM 2013, Turku, Finland, pp 208–222, 2013. doi: 10.1007/978-3-642-38613-8_15), we present the method via three example population protocols Angluin et al. (Distrib Comput 18(4):235–253, 2006). These were proposed as a theoretical framework for computability reasoning about Wireless Sensor Network and Mobile Ad-Hoc Network algorithms. Our examples present typical liveness and convergence requirements. We prove convergence results for the examples by integrated modelling and proof with Event-B/RODIN and TLA. We exploit existing proof rules, define and apply three new proof rules; soundness proofs are also provided. During the process we observe certain repeating patterns in the proofs. These are easily identified and reused because of the explicit nature of the reasoning.     

Composition mechanisms for retrenchment

Retrenchment is a flexible model evolution formalism that arose as a reaction to the limitations imposed by refinement, and for which the proof obligations feature additional predicates for accommodating design data. Composition mechanisms for retrenchment are studied. Vertical, horizontal, dataflow, parallel and fusion compositions are described. Of particular note are the means by which the additional predicates compose. It is argued that all of the compositions introduced are associative, and that they are mutually coherent. Composition of retrenchment with refinement, so important for the smooth interworking of the two techniques, is discussed. Decomposition, allowing finer grained retrenchments to be extracted from a single large grained retrenchment, is also investigated.